1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Discussion of the Background
Exhaust gas discharged from internal combustion engines, such as diesel engines, contains particulate matter (hereinafter, also referred to as “PM”). The PM has harmful effects on the environment and the human bodies, and thus the PM has been a recent issue.
In order to capture PM in exhaust gas to purify the exhaust gas, various honeycomb filters have been proposed as exhaust gas filters. These honeycomb filters include a honeycomb structure made of cordierite, silicon carbide, aluminum titanate, or the like.
A honeycomb structure including aluminum titanate has a melting temperature higher than that of a honeycomb structure including cordierite. It is therefore known that the honeycomb structure including aluminum titanate is less likely to be damaged by melting upon burning PM in the case where the honeycomb structure is used as a honeycomb filter. In addition, the honeycomb structure including aluminum titanate has a coefficient of thermal expansion lower than that of a honeycomb structure including silicon carbide. It is therefore known that the honeycomb structure including aluminum titanate is less likely to be damaged by heat applied upon burning PM even in the case where the honeycomb structure is used as a large-size filter.
US 2006/0021309 A1 discloses a honeycomb filter which includes a honeycomb structure mainly including aluminum titanate and showing small variation in the pore diameter distribution. The honeycomb structure is manufactured as follows: a material mixture mainly composed of Al2O2 and TiO2 is prepared; an oxide of a substance such as Bi, Ca, or Y is added to the material mixture; and the resulting mixture is fired.
FIG. 1A is a perspective view that schematically shows a conventional honeycomb structure mainly including aluminum titanate. FIG. 1B is a cross-sectional view (the D-D line cross-sectional view of FIG. 1A) that schematically shows a cross section of the honeycomb structure exposed by cutting the conventional honeycomb structure shown in FIG. 1A in parallel with the longitudinal direction.
FIG. 1B shows that a conventional honeycomb structure 410 mainly including aluminum titanate has cells 411 which are formed in the longitudinal direction with cell walls 413 interposed therebetween, and that the cell walls 413 separating the cells 411 functions as a filter.
More specifically, in the honeycomb structure 410, each of the cells 411 is sealed with a plug 412 at either one end of an inlet side (flow-in side) or an outlet side (flow-out side) of exhaust gas so that a check pattern is formed as a whole. Exhaust gas flowing into one cell is always caused to pass through the cell wall 413 which separates the one cell from other cells, and then is discharged from the other cells. When the exhaust gas passes through the cell wall 413, PM is captured in the cell wall 413, and thus the exhaust gas is purified.
The contents of US2006/0021309A are incorporated herein by reference in their entirety.